1. Field of the Invention
The present invention relates to a gas sensor for detecting the concentration of a specific gas component contained in a gas to be measured.
2. Description of the Related Art
In most automobiles, exhaust systems are employed by internal combustion engines, in which the exhaust systems comprise a gas sensor disposed for measuring the concentration of a specific gas component contained in the exhaust gas. The gas component is oxygen, nitrogen oxides and others. One such an example of the gas sensor is set forth in Japanese Patent Laid-open (unexamined) No. 2000-193629, for example.
The gas sensor disclosed by this publication is illustrated in FIG. 1, in which a gas sensor 9 comprises an element-holding body 913 which allows a sensing element 910 to be inserted and held therein. The gas sensor 9 has a heater 911 for heating up the sensing element 910. An atmosphere-side insulator 914 is disposed at a base end part of the element-holding body 913 to cover a base end part of the sensing element 910 in the longitudinal (axial) direction thereof.
As shown in FIG. 1, between a base end part 912 of the heater 911 and an inner wall surface 941 of the atmosphere-side insulator 914, a pair of contact fittings 92 are arranged so as to be opposed to each other, in which the contact fittings 92 are in contact with a pair of electrodes 920 of the heater 911 in such a manner that the base end part of the heater 911 be compressed. Each of the contact fittings 92 comprises a base plate 921 abutted on the atmosphere-side insulator 914 and an electrode contact member 922 located in front of the base plate 921. Each electrode contact member 922 is in contact with each electrode 920 of the heater 911, so that the heater 911 is electrically connected to an externally provided electric power source.
However, in cases where the pair of contact fittings 92 hold the base end part 912 of the heater 911 under pressure as shown in FIG. 2, the contact fittings 92 occasionally causes a state in which the atmosphere-side insulator 914 and each electrode 920 come contact with each other at two points therebetween. For example, in cases where deformations such as warpage occurred at the base plate 921, the inner wall surface 941 of the atmosphere-side insulator 914 and the base plate 921 are point-contacted, which causes each contact fitting 92 to be supported at two point contacts.
When the gas sensor 9 receives vibration from the outside under such a two point contact state, with the contact points between each contact fitting 92 and the atmosphere-side insulator 914 and between each contact fitting 92 and each electrode 920 as rotating fulcrums, the contact fitting 92 may vibrate laterally so that the contact fitting 92 is deviated from a central axis direction S of the heater 911, as shown in FIG. 3. As a result, if such a case happens, a contacted part between the electrode contact member 922 and the electrode 920 is worn away, resulting in that it is difficult to keep stable electrical conductance therebetween.